Red mud/biochar composite material (RMBC), which was applied as heavy metal passivator in this research, was prepared with red mud (the bauxite residue) and cornstalk under anoxic sintering condition. Based on the batch experiments in Pb contaminated soil, the passivating properties of several materials, including red mud (RM), biochar (BC), RMBC and phosphate-containing RMBC (PRMBC), were investigated in comparison with each other. Some interesting results are as follows: through anoxic thermal activation, a rough and porous structure of RMBC was obtained. Substances such as Fe₃O₄ and metal-organic complexes generated in RMBC provided effective sites for Pb passivation; and the mechanisms were speculated as the precipitation between Pb²⁺ and the carbonate (or hydroxide), as well as the complexation reaction between Pb and metal organic complexes through ligand bonding. The pot experiments showed the promotion effects of four passivators on the growth of red onion were in the following order: PRMBC > RMBC > BC > RM. PRMBC stabilized Pb content in soil significantly due to the formation of insoluble substances, with the minimum transfer factor and bioconcentration factor for plant growth. The evidences above implied the composite materials (PRMBC and RMBC) would be potential passivators for heavy metal-contaminated soil.

本研究以赤泥（铝土矿残渣）和玉米秸秆为原料，在缺氧烧结条件下制备了作为重金属钝化剂的赤泥/生物炭复合材料（RMBC）。通过在铅污染土壤中的批量试验，对比研究了赤泥（RM）、生物炭（BC）、RMBC和含磷酸盐RMBC（PRMBC）等几种材料的钝化性能。一些有趣的结果如下：通过缺氧热活化，获得了粗糙多孔的RMBC结构。RMBC中生成的Fe ₃ O _{4和金属有机络合物等物质为Pb钝化提供了有效位点；}其机理推测为 Pb ^{2+之间的沉淀}和碳酸盐（或氢氧化物），以及Pb与金属有机配合物通过配体键合的络合反应。盆栽实验表明，四种钝化剂对红洋葱生长的促进作用依次为：PRMBC > RMBC > BC > RM。由于不溶性物质的形成，PRMBC显着稳定了土壤中的Pb含量，具有最小的植物生长转移因子和生物富集因子。上述证据表明复合材料（PRMBC 和 RMBC）将成为重金属污染土壤的潜在钝化剂。